With the Euro IV standard on exhaust emissions from heavy goods vehicles coming into effect in 2005, devices for pollution control of NOx (or nitrogen oxides) have had to be put in place.
The system used by most heavy goods vehicle manufacturers for reducing NOx emissions to the required value consists in carrying out a selective catalytic reaction with reducing agents such as urea (“Urea SCR” or selective catalytic reduction using ammonia generated in situ in the exhaust gases by decomposition of urea).
In order to do this, it is necessary to equip the vehicles with a tank containing a urea solution, a device for metering the amount of urea to be injected into the exhaust line and a device for supplying, with urea solution, the device for metering the amount of urea to be injected. Generally, the supply device comprises a rotary pump driven by a motor.
The vehicles may be equipped with other liquid pumps, for example with a fuel pump, with a pump that may meter an additive directly into the fuel (diesel in particular) in order to reduce the emission of particulates, etc.
One feature in common to these “onboard” pumps lies in the fact that they should ideally have a limited size for optimum efficiency (both in terms of pressure and speed). These pumps are generally rotary pumps driven by a motor of any type, preferably a magnetically-coupled motor in order to avoid the use of dynamic seals.
Thus, Application PCT/EP2008/058943, in the name of the Applicant, the content of which is for this purpose incorporated by reference in the present application, describes a rotary fuel pump driven by a magnetically coupled motor. Such a pump delivers a controlled liquid flow, both the flow rate and pressure of which are controlled. One means for controlling the flow delivered is to implant a pressure sensor in the SCR system, at the pump outlet and to regulate the operation of the pump so that the pressure at the pump outlet follows a setpoint pressure value. The sensor may be implanted into the supply device of the SCR system. A solution of this type necessitates a manual assembly of the sensor to the device and therefore an additional assembly cost.
An alternative solution consists in attaching the pressure sensor directly to the pump. In this case it is the size of the pump/sensor assembly which is adversely affected. This solution also requires particular attention to the sealing at the pump/sensor interface, risks of liquid leaking from the inside to the outside of the pump being possible.
U.S. Pat. No. 5,120,201 discloses a liquid pump integrating a pressure sensor, but within the outlet pipe of said pump i.e. in a region where the pressure is not stable.